A large part of a reason why there is so much cartel traffic and smuggling activity along our southern border is the same reason there is borderline civil war and widespread violence in Mexico right now.
America loves drugs. We love can't get enough of the stuff. From homeless Johnny be hitting crack on the corner of 32nd Street to daddy's own little girl smoking grass with Drop out Billy Bob after school.
Hell even high in investors and our cherished celebrities go for the more expensive drugs.
As for the social immigrants seeking a better future, or even an escape from living in a war zone, where else would you go? South? South America is ripe with it's own issue's and what are you going to do ? Go to Europe?
America is just the closest 1st world country to get into, and somewhat one of the easier one's to at that. Europe seems to be having similar issues with their Muslim populations right now, especially in dealing with "economic" immigrants, it seems the problems there are reaching a head, and seem eerily familiar with our own immigration debate here.